The conventional method of placing a heater which is the heat source of the cathode of an electron gun of a cathode ray tube into a sleeve described below.
As shown in FIG. 1A, a supporting piece 12 secured to a bead glass 11 is eccentric from the center of a sleeve 14 by as much as the thickness of a U shaped connecting piece 15 of a heater. The sleeve 14 is supported by a protection tube 13. In such a state, a terminal 16a of a heater 16, which is constructed as shown in FIG. 1B, is welded to the side of the connecting piece 15 that is disposed nearer to the center of the sleeve 14, so that the heater 16 is placed at the center of the sleeve. In the succeeding processes, a bridge portion B of the U shaped connecting piece 15 is removed as shown in FIG. 1B.
In such a heater supporting structure, when the heater supporting piece 12 is secured to the based glass 11, the heater connecting piece 15 has to be disposed eccentrically relative to the center of the sleeve 14 by as much as its own thickness, and this requires a critical dimensional control. Further, when the heater 16, which is welded to a heater connecting piece 15, is inserted into the sleeve 14, and when the heater connecting piece 15 is welded to one side of the heater supporting piece 12, the heater 16 is placed at the center of the sleeve 14, in the left-right direction of FIG. 1A, due to the fact that the connecting piece 15 makes facial contacts to the supporting piece 12 on the left and right sides as shown in FIG. 1A.
However, in the up and down direction of FIG. 1A, there is no way of preventing movement of the connecting piece 15 relative to the supporting piece 12, and therefore, the positional uniformity depends on the skillfulness of the worker.